It is known, as for example from U.S. Pat. No. 3,351,836, to power a windshield-wiper motor from an oscillator having an RC circuit that can be adjusted to vary the period of the oscillator. Normally the resistance element is either made variable, or any of several different resistances can be switched in to vary the speed. Such an arrangement has the advantage of extreme simplicity, yet rarely offers a wide variation in wipe rate. Furthermore the provision of a potentiometer to achieve stepless variation has been found disadvantageous in that such circuit elements frequently have a limited service life, especially in the normally harsh environment of a motor vehicle.
Accordingly a system has been proposed in the German-language publication Elektor (April 1980, pages 34-39) to use a wholly electronic arrangement which is controlled by a single switch in a rather complicated manner. If the switch is actuated after the ignition is turned on the wipers operate continuously at maximum speed. If the switch is turned off, a counter in the control circuit begins to count out the interval during which a memory of the circuit is fed "0" pulses from the counter. As soon as the switch is again actuated, a "1" pulse is fed into the memory. This "1" pulse triggers the wiper which makes one sweep back and forth over the windshield and at the same time restarts the counter at zero. Once again the counter generates a series of "0" pulses which are monitored by the memory until the previously read in "1" pulse reappears, at which time the wiper is again actuated. Thus the time interval between the two actuations of the switch constitutes the time interval between subsequent successive wipes of the windshield.
Such an arrangement is interesting in that it does allow the user to exactly program the windshield wipers. The circuit itself is relatively complex and is energized, that is connected to the vehicular electrical system, at all times so that it represents quite an energy drain. Furthermore it is relatively difficult to combine such complicated circuitry with a simultaneous wash-and-wipe function.